This invention relates to instruments for measuring and recording the infra-red spectrum from heat sources, and, more particularly, to passive devices for measuring and recording the thermal fluence from radiative heat sources.
At present, these type of measurements are made with electronic calorimeters. These instruments require a calorimeter element wired to a preamplifier which in turn is wired to a tape recorder to make a permanent record of the measurements. The calorimeters normally used for this type of measurement, measure the thermal flux (time varying heating rate) from the radiation source and not the thermal fluence which is the data that is of paramount interest in most nuclear effects and other intense thermal radiation testing.
There are many other drawbacks to the use of the electronic instruments, not the least of which is the high cost of these instruments which, not unusually, run as high as $2,000 to $3,000 per recording channel. As a result of this high cost, only a small percentage of the desired locations on the item under test are normally instrumented to record the incident thermal radiation during a test. To make matters worse, frequently the signal-to-noise ratio of the output signal from the calorimeter is low, and in some cases so low that valid data is recovered by less than 50% of the recording channels. Additionally, data recovery is effected by a variety of failures such as broken wires, preamplifier failure, calorimeter burnout, and tape recorder saturation, not to mention the tedious calibration and checkout procedure necessary to ready these instruments for use in the tests.
It would be desirable to have a transducer for these applications that is less expensive than electronic calorimeters, more reliable, not limited by the electronics, small in size and can be used to map large surfaces such as aircraft structures to record the variations in the radiation incident on all parts of that structure, and one that provides quick, on the spot test results without the need for computer evaluation of the data from magnetic tape. The present invention disclosed herein presents such a transducer.
In accordance with the preferred embodiment, the transducer includes a selected number of polystyrene pieces each having a selected thickness and geometric shape for sensing thermal radiation fluence from radiative heat sources. These pieces are selectively stacked one on top of the other for providing at least partial thermal shielding from one layer of the stack to the next. Also included is fastening means for holding the pieces in position one with respect to the others.
The method of the preferred embodiment for measuring the thermal radiation fluence from a radative heat source comprises measuring selected dimensions of each of the pieces of the transducer after exposure to the radiative source. These measurements are then operated on mathematically to obtain a measure of the intensity of the fluence to which the transducer was exposed.